1. Field of the Invention
The present invention generally relates to a cleaning sponge roller for removing fine particles such as abrasive grains, swarfs and scobs off the surface of a material. More particularly, the present invention relates to a sponge roller for cleaning a material surface in the process of producing substrates such as magnetic recording aluminum discs, semiconductor silicon wafera, and the like. The present invention also relates to a mold for forming the sponge roller.
2. Description of Related Art
A process of producing a hard disc, a silicon wafer, or the like (including, but not limited to, a glass disc, a semiconductor element which is subjected to a chemical mechanical polishing (CMP) work, a photomask, a liquid glass substrate, etc.) requires a step of high precision abrasion or xe2x80x9cpolishing,xe2x80x9d which provides a surface of the disk or wafer with an extremely high precision finish. The high precision finish is achieved by polishing the surface with abrasive grains such as silicon oxide particles, alumina particles or cerium particles. When this step is complete, however, the surface is contaminated with the residue of the polishing, such as grains, swarfs and/or scobs. The residue must be cleaned before the material can undergo a subsequent step.
Several conventional cleaning methods have been known. The RCA cleaning method, one of the conventional methods for cleaning silicon wafers, uses a mixture of aqueous ammonia and hydrogen peroxide and a mixture of dilute hydrofluoric acid, hydrochloric acid and hydrogen peroxide. Another conventional method for cleaning a hard disc, silicon wafer, etc. is a method of using a cleaning sponge roller made of a polyvinyl acetal-based (xe2x80x9cPVAt-basedxe2x80x9d) porous material.
For example, as shown in FIG. 6, a sponge roller 51 is used to clean a surface 9a of a material 9. The sponge roller 51 typically includes a roll body 3 having a peripheral area 3a and a plurality of protrusions 53 integrally protruding from the peripheral area 3a. A top portion 53b of the protrusion 53 is brushed in a direction indicated by an arrow against the surface 9a of the material 9 by pressing the protrusions 53 onto the surface 9a and subsequently separating the protrusions 53 from the surface 9a. The pressing and separating motions are repeated. As a result, the material 9 is brushed with the sponge.
As shown in FIG. 6, the protrusions 53 are generally columnar shaped, having almost the same cross-sectional shape from a base end surface 53a of the protrusion 53 to a top end surface 53b. When such columnar shaped protrusions brush against the surface 9a, a tension acting on the protrusion 53 concentrates at the base end surface 53a and causes the base end surface 53a to be locally deformed in its vicinity. In addition, since the peripheral area 3a is not completely flat but inclines toward the opposite side of the protruding direction of the protrusion 53 in a shape of a circular arc, it is not cleanly deformed in a lateral direction compared to a case wherein the protrusion is attached to a completely flat surface. Therefore, a front-end portion 55 connecting the base end surface 53a with the periphery 3a of the roll. body 3 becomes easily broken.
Such a problem can be solved by forming the protrusions in a larger size to enhance the strength thereof. However, this creates another set of problems in that a desired brushing effect is not obtained and the cleaning effect may be lowered.
It is an object of an embodiment of the present invention to provide a PVAt-based sponge roller with an improved durability without decreasing the quality of cleaning performance.
To attain the object described above, in accordance with one embodiment of the present invention, a cleaning sponge roller has a generally cylindrical roll body and a plurality of protrusions molded integrally on the periphery of the roll body. The periphery of the roll body rotates and brushes polishing residue off the material to be cleaned. Each of the protrusions of the roll body has a tapered protruding base portion extending from the periphery of the roll body, and a protruding end portion having generally the same sectional shape extending from the top end of the protruding base portion to the top portion of the protruding end portion. The protruding base portion may be formed in a shape of generally truncated cone. The protruding end portion may be formed in a generally columnar shape or a generally cylindrical shape.
With the above construction, the protruding base portion of the protrusion has an outer surface formed in a divergent shape toward the periphery of the roll body and a sectional area of the protruding base portion attains a maximum at the base end (border between the periphery of the roll body and the protruding base portion) and gradually decreases toward the protruding end portion. Therefore, when each of the protrusions is pressed in the lateral direction, a stress concentration in the vicinity of the base end of the protruding base portion where the tension is concentrated is dispersed in the whole protruding base portion. Thus, the protrusion according to the present invention is significantly more durable than the protrusions of conventional sponge rollers.
Since the durability of the protrusions can be improved without exerting any influence on the shape of the protruding end portion, the protruding end portion that is to be contacted with the material to be cleaned can readily be formed into a size and a shape that are most suitable for brushing.
In accordance with one embodiment, a cleaning sponge roller is formed from a polyvinyl acetal-based porous sponge that is obtained by reacting a viscous mixed solution containing raw materials in a mold. The mold corresponding to the sponge roller with the above construction comprises a first space for forming a roll body and a plurality of second spaces for forming protrusions. Each of the second spaces comprises a base portion forming space for forming a protruding base portion and an end portion forming space for forming a protruding end portion. The base portion forming space communicates with the first space on one side and the end portion forming space on the other.
The base portion forming space has an inclined surface extending toward the first space from the end portion forming space. In the production of the sponge roller, the mixed solution is poured into the first space and then the solution flows into each second space from the first space. In this case, since the base portion forming space of the second space has an inclined surface extending toward the first space, the mixed solution flows smoothly into the end portion forming space guided by the inclined surface of the base portion forming space. At the same time, an air in the second space moves smoothly to the first space from the end portion forming space and then is released in the air from the first space. Consequently, the mixed solution can be securely charged to the terminal end of the second space, thereby making it possible to reduce the production cost due to an improvement in yield.
The height from the periphery of the roll body to the top end of the protruding base portion is preferably not more than one-half, and more preferably not less than one-fifth times as long as that of the protrusion.
When the height of the protruding end portion exceeds one-half times as long as that of the whole protrusion, there is a possibility that the deformation amount of the protruding end portion is reduced and the brushing effect on cleaning becomes insufficient. On the other hand, when the height of the protruding end portion exceeds one-fifth times as long as that of the whole protrusion, there is a possibility that sufficient strength cannot be obtained.
The crossed axes angle between a straight line, which connects the base end and top end of the outer surface of the protruding base portion, and the periphery of said roll body in an arbitrary section is preferably from 30xc2x0 to 60xc2x0.
When the crossed axes angle is smaller than 30xc2x0, there is a possibility that the protruding base portion may extend largely toward the periphery and an area of the lower end surface of the protruding end portion may increase, thereby limiting the total number of the protrusions which may be formed on the periphery of the roll body. On the other hand, when the crossed axes angle exceeds 60xc2x0, there is a possibility that sufficient strength may not be obtained.
Furthermore, the shape of the outer surface of the protruding base portion may also be a linear inclined surface or a curved inclined surface.